As the utilization of lenses or the like, particularly contact lenses, becomes more widespread, and as the production of lenses, particularly contact lenses, becomes more sophisticated, it is desirable to minimize fabrication difficulties and complexities in order to produce lenses economically. This is particularly true with respect to the production of all of hydrophilic (soft), silicone, and hydrophobic (hard) contact lenses.
The present invention relates to procedures and apparatus facilitating production of lenses. While the invention is particularly applicable to the manufacture of contact lenses, the word "lens" per se as used in the present specification and claims is not restricted to contact lenses, but also includes other types of lenses, mirrors, and the like. The invention is particularly useful in association with the production of multifocal contact lenses. While not restricted to multifocal contact lenses, according to one aspect of the invention multifocal contact lenses--and procedures and apparatus for the manufacture thereof--are made more universal, while according to another aspect of the present invention the production of high quality multifocal contact lenses is facilitated.
In the production of multifocal lenses, such as shown in U.S. Pat. No. 3,471,976 (the disclosure of which is hereby incorporated by reference herein) it is important to start with a single vision lens having the same power throughout. In the manufacture of single vision lenses the base curve of the lens is cut first, and then wax holds the lens to a convex-surfaced chuck, and the power curve of the lens is cut while held by the chuck. Then polishing of the lens, particularly the power curve thereof, is practiced, usually while the lens continues to be held by the chuck. Polishing is conventionally practiced by placing a polishing-holding material (such as cotton or chamois) on a flat sponge, with appropriate polish held by the material, and the polish is brought into contact with the lens. The sponge distorts as the lens is pressed into contact with it, and the sponge thereby provides a biasing force maintaining contact between the polish and the lens. A flat sponge is used since the lens may have virtually an infinite number of different power curves, and a flat sponge can accommodate all such curves so that only one polishing tool is required.
While prior procedures do effect polishing of the lens, a significant portion of the central area of the lens may be worn away during polishing, resulting in a non-uniform product. If this occurs, the lens is not appropriate as a single vision lens, and is not appropriate for manufacture into a multifocal lens such as provided in said U.S. Pat. No. 3,471,976.
According to one aspect of the present invention it has been determined that non-uniform polishing of the lens occurs since the flat sponge is depressed to a greater degree at the portion thereof in operative association with the center of the lens than are portions thereof in operative association with the periphery of the lens. Since the compression is greater at portions of the sponge associated with the central area of the lens, the pressure applied by the sponge to the polish in contact with the central area of the lens is also greater. Thus non-uniform wear during polishing can occur.
According to the present invention it is possible to polish a lens (particularly a dehydrated hydrophilic, a silicone, or a hard contact lens) with complete uniformity of wear during polishing. The polished lens is entirely suitable for ultimate production of a multifocal lens. This is accomplished by utilizing a pressure responsive flexible sheet mounting polishing compound thereon, and mounted to flex under the influence of fluid pressure without substantial distortion of the sheet itself, and fluid pressure means for biasing the sheet so that the polishing compound associated with it makes contact with the lens surface brought in contact therewith with a uniform force distribution. The surface of the lens to be polished is brought into contact with the polishing compound associated with the flexible sheet, causing the sheet to flex, and fluid pressure is applied to the sheet counteracting the flexing as a result of lens contact. Relative rotation between the lens and sheet is then effected so that all portions of the lens surface in contact with the polishing compound are polished to the same extent.
The flexible sheet preferably is made of a generally non-resilient material, such as a material having the general resiliency properties of a sheet of polytetrafluoroethylene. The fluid pressure may comprise a housing having an open face covered by the flexible sheet and defining a substantially fluid-tight volume, with fluid filling the volume and applying a force to the sheet. The fluid may be a generally incompressible liquid, such as oil. (The terms "non-resilient" and "incompressible" are of course relative terms, and are to be interpreted in the present specification and claims to be consistent with the achievement of the ultimate results desired in the practice of the invention.)
According to another aspect of the present invention, it is possible to effectively produce a multifocal hydrophilic or silicone contact lens in a manner consistent with conventional procedures for properly fitting a wearer with contact lenses. Often it is advantageous and less expensive for a practitioner to fit a multifocal lens patient with a single vision contact lens first to be sure that the lens is comfortable, positions properly in the patient's eye, and has the correct power.
Utilization of the single vision contact lens can also provide a good means of determining the distance and near power required by the patient. Since the production of two identical lenses is difficult, it is advantageous (and less expensive) to use the same hydrophilic or silicone contact lens that has been fitted and is known to possess the appropriate characteristics as the starting lens in the production of a multifocal lens. Heretofore it has not been practical to follow such a procedure with hydrophilic contact lenses, however, since the lens must be hydrated to be fitted into the patient's eye, and once hydrated will become grossly distorted if dehydrated, and therefore cannot be processed properly. Such procedure has also been difficult for silicone lenses since they are difficult to grind without distortion.
The word "silicone" as used in the present specification and claims means silicone or other soft or pliable materials suitable for use as contact lenses.
According to the present invention, a method of forming a hydrophilic or silicone contact lens having desired distance and intermediate powers is provided, overcoming the limitations inherent in the prior art. With respect to hydrophilic lenses, the method is practiced by (a) hydrating the hydrophilic contact lens; and (b) without distorting the lens grinding the lens to that it has the desired distance and intermediate powers. Step (a) is practiced by fitting a single vision hydrophilic lens in a wearer's eye, and step (b) is practiced by acting on the single vision lens to provide a multifocal hydrophilic contact lens suitable for use by the wearer. It is also possible at any time that it is necessary to change the parameters of the multifocal lens to further act upon it so that it is suitable for use by the wearer.
The step (b) in the practice of the method according to this aspect of the invention may be accomplished in a variety of manners. For instance the lens may be frozen after hydration, and ground while in the frozen condition. Alternatively, the lens may be dehydrated while clamped between a pair of clamping members which prevent distortion of the lens, and the lens ground once dehydrated. Another alternative is to provide a chuck having a surface with the same curvature as the base curve of the hydrophilic contact lens, and to bring the lens--while hydrated--into operative contact with the chuck curved surface so that the chuck holds the lens in place, and the lens can then be ground while hydrated and held by the chuck. Yet another alternative is to provide a hard contact lens having a power curve substantially the same as the base curve of the hydrophilic lens, and to bring the hydrophilic lens--while hydrated--into contact with the hard contact lens. The hard contact lens is then held by the grinding apparatus in the manner disclosed in said U.S. Pat. No. 3,471,976, and hydrophilic lens is ground while in contact with and held by the hard lens.
For both hydrophilic and silicone contact lenses a method of forming a multifocal lens is provided according to the present invention by acting on the lens so that it is capable of accepting activity from a grinding apparatus, and then grinding the lens without distortion. It is made capable of accepting grinding activity by properly backing it or freezing it.
It is the primary object of the present invention to facilitate the production of high quality lenses, particularly hydrophobic, silicone, and hydrophilic contact lenses. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.